Hey there! If you’re working in industrial power, telecom, or even data center hardware, you’ve probably hit a point where one power supply just isn’t enough. Maybe you need extra output for a new server rack, or you want to add redundancy so if one unit craps out, the whole system doesn’t go dark. That’s where parallel power supplies come in— and when your gear uses PFC (power factor correction) tech, there’s a specific set of rules to make that work right. As someone who’s been supplying PFC power supplies for years, I’ve seen way too many folks skip the basics here and end up with weird glitches, uneven load sharing, or even fried units. Let’s break this down like we’re chatting over coffee, no fancy textbook jargon that makes your eyes cross. PFC Power Supply
First, let’s refresh what a PFC power supply actually does, for anyone who might be new. Regular AC power from the wall isn’t a perfect sine wave, and old power supplies used to draw current in big, lumpy bursts that messed up the grid’s power factor (think: wasting energy, getting fined by utility companies for bad power quality). Active PFC (the kind we supply) fixes that by smoothing out that current draw so it’s in sync with the AC voltage, knocking power factor up to 0.95 or higher— that’s huge for cutting energy bills and complying with standards like 80 Plus. Now, when you parallel two or more of these units, it’s not just plugging them into the same bus and calling it a day. If they “fight” each other, you’ll get one unit carrying almost all the load and the other barely doing anything, or worse, current surging between them. That’s why load sharing is the whole name of the game here.
Wait, what’s load sharing exactly? It’s the process where all parallel PFC units split the total system load evenly, right up to their combined max output. So if you have two 1000W PFC supplies, a 1500W total load means each carries 750W. Easy in theory, but PFC units have their own control circuits that can throw this off. Let’s get into how that works. Most modern parallel-ready PFC power supplies use what’s called “droop current sharing” or “average current sharing”— two main methods, and I swear there’s a big debate among engineers about which is better, but both work if set up right.
Droop current sharing is the simpler one, honestly, and a lot of entry-level parallel supplies use it. Here’s the gist: each unit has a tiny output resistance built in (it’s not a physical resistor, it’s part of the control loop). If one unit starts outputting a little more current than the others, its internal resistance bumps up a bit, which brings its voltage down just enough so the other units pick up the slack. It’s like a group of people carrying a heavy couch— if one person starts lifting too hard, they adjust their grip to even it out. The problem with droop is that it’s not perfect. There’s a tiny voltage drop across each unit’s internal resistance, so the total output bus voltage is a little lower than a single unit would put out. That’s why droop works best for systems where you don’t need super precise load matching— like a warehouse backup system where a 5% difference in load is no big deal.
Average current sharing is the more precise method, which is what most of our mid-to-high-output parallel PFC supplies use. Here, every unit in the parallel chain talks to each other over a simple communication cable (it’s usually a 3 or 5-pin connector, super standard) to share a signal that says, “Hey, I’m currently carrying X amount of current, what’s everyone else got?” The control circuits then adjust each unit’s output to match the average current of the group. So if one unit is at 800W and another is at 700W, the third will nudge its output down a little, and the first might nudge up, until all three are at a smooth average. This is way better for telecom or data centers, where you need consistent load distribution to keep your units running cool and extend their life.
Now, the big rules you have to follow when parallel PFC supplies— I can’t stress these enough, because I’ve had a customer call me panicking at 2AM because they didn’t do these and lost two units. First, all the parallel units have to be the same model, same output voltage, same max current. That’s non-negotiable. You can’t parallel a 12V 100A PFC supply with a 12V 80A unit and expect it to work right. The 80A one will hit its current limit and shut down before the 100A one is even loaded properly, which wastes capacity and is a fire hazard. Even if they’re from the same brand, different revisions of the same model might have different firmware, so double-check that too. We always test every unit from our production line to make sure their firmware matches for parallel use, so that’s one less thing you have to worry about when you buy from us.
Second, the communication cable for average current sharing— you can’t just daisy-chain it randomly. You have to connect it in a linear chain, not a star (like, plug Unit 1 to Unit 2, Unit 2 to Unit 3, not all units to a central hub). And make sure the cable length is consistent for every connection, and no extra cables hanging loose causing interference. I’ve seen guys use a random Ethernet cable for this (it’s not made for control signals) and get noise on the communication line, leading to load sharing glitches. We supply the correct parallel cables with every multi-unit order, so just use those— it’s not worth cutting corners here.
Third, don’t mix active and passive PFC supplies in parallel. Passive PFC is the old, bulkier kind that uses inductors to correct power factor, and it’s way slower at adjusting current. If you parallel an active PFC (the kind we sell) with a passive one, the passive unit can’t keep up with the active one’s control loops, so it’ll either hog all the load or sit idle. Stick to active PFCs for parallel setups, they’re designed for that.
Now, what about redundancy? That’s the biggest reason people parallel supplies, right? You want if one unit dies, the others can pick up the extra load without shutting down the whole system. For N+1 redundancy, you have total output capacity equal to (N units -1) times the max output. So if you need a 2000W total load, you can run three 1000W units: two carrying 1000W total, the third as a backup. If one fails, the other two can take up the slack. Just make sure your parallel PFC supplies are rated for N+1 operation— some units will shut down if you exceed their max current, so our parallel-ready models are rated for that extra load. We have a lot of telecom clients who use 3+1 parallel PFC setups in their cell towers, so if one unit takes a lightning hit, the others keep the tower running.
Wait, another thing: hot-swapping. Can you replace a failed parallel PFC supply without turning off the whole system? Yeah, most modern parallel active PFC supplies support hot-swap, but you have to follow the right steps. First, make sure the new unit is identical to the ones in the system, same firmware, same output. When you plug it in, the control loop will detect it, adjust the load to include the new unit, and split the work evenly. Don’t just yank a dead unit out— even with hot-swap, the bus voltage can dip if you do it wrong, so we always recommend waiting 10 seconds after turning off the power to the failed unit before disconnecting it, and turning the new unit on and letting it sync for 30 seconds before putting the system back to full load.
I get it, there’s a lot to wrap your head around if you’re new to this. Let’s talk about a common mistake I see all the time: people think adding more units to parallel means more capacity, and that’s true, but only if you do it right. Last year, a customer bought four of our 1500W PFC supplies, thought he could pair them with two 1000W units from another brand to get 8000W total. Turns out the other brand’s units didn’t have compatible parallel control loops, so the four good units were carrying 7500W total, and the two off-brand ones were doing nothing. He had to send the off-brand ones back and order two more of our units, so he ended up with six units total— worked out great, but he wasted a week of downtime because he tried to cut costs with mismatched gear.
Another tip: monitor your parallel system. A lot of our PFC power supplies come with remote monitoring ports, so you can check load levels, unit temperature, and fault status from your office. If one unit starts carrying 10% more than the average over a few days, that’s a sign it’s failing and needs replacement before it craps out. We offer basic monitoring software with all our parallel PFC orders, so you don’t have to build something from scratch.
What about power factor in a parallel setup? Does running multiple PFC supplies in parallel mess with the overall power factor? Nope, not if they’re working right. Each individual PFC supply corrects its own current draw, so the total system power factor is still around 0.95, same as a single unit. That’s a huge win for your energy bills— a data center with 20 parallel PFC supplies is still getting that efficient power draw, no extra strain on the grid.
Wait, let’s address a question I get all the time: can you parallel different wattage units as long as they’re the same model? Let’s say two 1000W and one 800W of the same series. Technically, the average current sharing loop would adjust, but you’ll end up with the 800W unit running at 100% load all the time, which shortens its life. Our recommendation is always to use identical units in parallel, so each runs at a comfortable 50-70% load, which is the sweet spot for reliability. That’s how we design our parallel PFC supplies, so that load distribution stays even even as they age.
Now, if you’re putting together a parallel PFC system, what order do you hook everything up? Let’s run through a quick step-by-step for a small 2-unit setup, super simple. First, turn off all power to the whole system, including the AC input to the supplies. Then, connect the parallel communication cable between the two units, same as we talked about earlier (linear, matching length). Next, connect the DC output bus: attach the positive terminals of both units to the positive bus bar, negative to negative, use thick enough wire to handle the total current— don’t use thin 18 gauge wire for a 2000W system, that’s a recipe for voltage drop and overheating. Then connect the AC input lines to both units, making sure phase order matches (we mark L, N, G on all our supplies so that’s easy). Then turn on the AC input first, wait 10 seconds, then turn on both unit’s power switches. They should fire up, sync over the communication cable, and start splitting the load evenly within a few seconds. If not, check the communication cable, make sure the units are identical, and check for fault codes on the display (our units have a tiny LED that flashes if something’s wrong, super easy to read).
I’ve been in the power supply game for over a decade, and the biggest takeaway I want you to have is this: parallel PFC supplies aren’t rocket science, but they do require paying attention to the small, specific details. Cutting corners on matching units, using the wrong cables, or skipping load testing will cost you way more in downtime and replacements than just doing it right the first time. When you source your parallel PFC supplies from a supplier that designs their units specifically for parallel operation (like us), you skip all the headaches— we test every pair or set before shipping, include all the right cables and monitoring tools, and our support team is available 24/7 if you run into a problem.
If you’re working on a project that needs parallel power supplies— whether it’s a new industrial automation system, a telecom tower, or a data center rack— and you want to make sure it’s set up right, hit us up to chat through your needs. We don’t do one-size-fits-all, so we can help you pick the right number of units, right wattage, and even custom configurations if your project has specific requirements. No salesy jargon, no pushy tactics, just honest advice based on what’s worked for our customers over the years.
Before I wrap up, let’s make sure I didn’t miss anything important. Oh, right— isolation! When you parallel power supplies, the DC outputs need to be isolated from each other and from ground, right? All our active PFC supplies have isolated outputs, so you don’t have to worry about ground loops causing current to circulate between units. That’s a key feature that differentiates our parallel-ready models from regular single-unit PFC supplies. A lot of cheap parallel units skip isolation, so you get a ground current that wastes power and can damage equipment, so always check for that.
Another thing: temperature. Parallel units run hotter than single units, since they’re sharing load, so make sure your system has enough airflow. We rate our parallel supplies for 50°C ambient temperature, and if you’re installing them in an enclosed rack, add extra fans to keep the air moving. Overheating is the number one cause of power supply failure, so don’t ignore ventilation.
Alright, that’s a lot to take in, but it’s all the stuff you actually need to know when working with parallel PFC power supplies. If you’ve got questions about load sharing, choosing the right units, or setting up your system, reach out to our team to discuss your specific application. We’ve worked with every type of industry, from small machine shops to large data centers, so we can help you get a reliable, efficient parallel power setup that works for you.
Open Frame Switching Power Supply References
- "Power Supply Parallel Operation: Concepts and Practices," Power Electronics Technology, 2021.
- Active Power Factor Correction for Parallel Power Supplies, International Journal of Power Electronics, 2019.
- Redundant Power System Design for Industrial Applications, IEEE Transactions on Industrial Informatics, 2020.
Guangzhou Kaihui Electronics Co., Ltd.
Guangzhou Kaihui Electronics Co., Ltd. is one of the most professional pfc power supply manufacturers and suppliers in China, specialized in providing the best customized service. We warmly welcome you to buy high quality pfc power supply made in China here from our factory.
Address: 2F BLDG8, Standard Ind.Park, Dongchong Town, Nansha District 511453, Guangzhou, Guangdong, China
E-mail: amy@gzkaihui.com
WebSite: https://www.kaihuipowersupply.com/
